Immigration Offices Holidays July 2017
I just called the gov't hotline at 1111 and asked about the holidays for July.
The immigration offices country wide will be closed on
10th July - Substitution Day for Asalha Bucha Day
28th July - H.M King Maha Vajiralongkorn's Birthday
Be advised that some thai consulates are closed on the 11th as well because it is a Substitution Day for Buddhist Lent Day BUT the immigration offices INSIDE the country are not closed. (or that's what the gov't hotline told me ;) )
TLDR : Answer Summary
In July 2017, immigration offices in Thailand will be closed on July 10th for Asalha Bucha Day and July 28th for King Maha Vajiralongkorn's Birthday. Some Thai consulates will also be closed on July 11th due to being a substitution day for Buddhist Lent, but immigration offices within Thailand will remain open.